Japanese Patent Publication No. 11-308850 discloses a linear motor which includes a stator and a movable element so that the movable element may reciprocate with respect to the stator, and further includes an armature disposed on one of the stator and the movable element and a permanent magnet magnetic pole row disposed on the other of the stator and the movable element. The armature of the linear motor has an iron core having three or more magnetic pole portions arranged along a moving direction of the movable element, and armature windings of three phases respectively wound around the three or more magnetic pole portions of the iron core. The permanent magnet magnetic pole row has a frame of a nonmagnetic material and a plurality of permanent magnets disposed in through-holes formed in the frame. The plurality of permanent magnets are disposed at a given interval in a row along the moving direction of the movable element so that north poles and south poles may alternately be arranged. The permanent magnet magnetic pole row faces the magnetic pole portions with a given gap therebetween. To reduce the cogging torque, in this linear motor, a length W1, as measured in the moving direction, of each of two permanent magnets which are respectively disposed at either end of the permanent magnet magnetic pole row is defined to be less than a length W, as measured in the moving direction, of the remaining permanent magnets, and that a ratio W1/W of the length W1 to the length W is defined as 0.5<W1/W<0.6. In addition, when a pitch between centers of two adjacent magnetic pole portions of the plurality of magnetic pole portions constituting the armature is defined as τs, and a pitch between the center of one of the two permanent magnets respectively disposed at either end of the permanent magnet magnetic pole row and the center of the permanent magnet adjacent thereto is defined as λ′, a ratio λ′/τs of the pitch λ′ to the pitch τs is defined as 0.9<λ′/τs<1.0.
However, it is not possible to sufficiently reduce the cogging torque in conventional linear motors.